Request signing

Hi Eric,

This pull request gets Google Maps for Business signing working, along with a small testing framework that allows somebody with their own signing key to test them without having to insert their credentials into the code.

I've only written a test for geocoding so far.

The changes are way smaller than the whole-file diffs make it look, really all I am doing is adding the required client=gme-xxxx to the URL automatically before it gets signed, which is what my issue #5 is all about.

The .gitignore change is so that the file containing the signing information is ignored by git.

Cheers,

R.